A wide variety of surgical techniques and associated instrumentation systems have been developed for correcting degenerative disc disease, spondylolisthesis, spinal deformities, or other spinal conditions through minimally invasive or invasive spinal surgery. Spinal correction during surgery may be performed by a variety of methodologies that may frequently require stabilizing a portion of the spine to allow bone or other tissue growth between vertebral bodies such that a portion of the spine is stabilized into a solitary unit and/or specified shape.
Numerous surgical instrumentation systems have been developed and commercialized for stabilizing and correcting spinal conditions and/or deformities. In one of the most popular types of spinal stabilization systems, pedicle screw and rods systems, two or more screw assemblies are secured into bony structures of the a patient's vertebrae, and a rod or other device is connected between the screw assemblies, typically disposed longitudinally along the length of the spinal segment to anchor the two or more vertebral bodies relative to each other. The rod can be arranged in a variety of positions and/or configurations (including the use of multiple rods and/or cross-bars, where desired) according to the patient's anatomy and/or the correction desired. In many cases, the patient's anatomy and/or the desired surgical correction required can require aligning one or more rods and associated pedicle screws at various multi-axial angles and/or orientations along the length of the portion of the spinal segment.
Unfortunately, existing pedicle screw systems are typically rather large and bulky, and the modularity and/or flexibility designed into the components in many of these systems can render the systems difficult for a surgeon to use effectively. For example, the various feature that facilitate the assembly of different size and/or shape rod and screw constructs, and eventual “locking” of the components together (i.e., the pedicle screw assembly and the rod) to specified orientations, shapes and/or multi-axial angles (prior to fixation) can be difficult and/or impossible to assemble within a wound. Moreover, where components have been preassembled, such as where a pedicle screw subassembly includes a tulip head pre-connected with a mono-axially and/or poly-axially adjustable bone screw shank, the tulip head will desirably move relative to the shank. In many such instances, however, manufacturing and/or assembly of the tulip head, relevant inserts and/or the shank itself can result in a subassembly where the shank/head is loose and can “flop” around, making it extremely difficult for the surgeon to assemble the construct and/or tighten the remaining components together. Alternatively, the tulip head may be too tight relative to the shank, rending it difficult and/or impossible for the surgeon to adjust the assembly by hand (prior to fixation).
Assembly difficulties can also be experienced when positioning and/or connecting one or more of the rods to the implanted pedicle screws. Because patient anatomy is unique, which can often be compounded by significant preoperative deformity, rarely do the implanted pedicle screw heads conveniently “line up” in a uniform manner. In fact, implanted screws can often be significantly displaced from adjacent screws. Also, when the surgeon places a rod into pedicle screws, the rod may slide to an undesired position or otherwise be displaced or moved before the surgeon is ready for tightening the remaining components together. This may inconvenience the surgeon and might require surgical assistants, technicians or staff members to properly orient the pedicle screw assembly and maintain the rod position while the surgeon fully tightens all of the components together. In many cases, the proper fixation of the stabilization system particularly depends on the surgeon and/or staff to properly assemble the rod and the pedicle system, orient the pedicle screw system, and/or position the rod properly to effectively lock the components together with the set screw, otherwise no amount of tightening the set screw will fully or effectively lock the pedicle screw assembly together—i.e., the floppiness remains and the rod may move axially to an undesired position.